Self-crimping filament process



Feb. 24, 1970 R. M. CHAPMAN ET AL 3,497,585

SELF-CRIMPING FILAMENT PROCESS Filed June 9, 1966 ,0"! 2 T 1 W2 3 I6 3 3 INVENTORS ODNEY, M. CHAPMAN ILBU United States Patent 3,497,585 SELF-CRIMPING FILAMENT PROCESS Rodney M. Chapman, Kinston, and Wilbur J. Privott, Jr., Raleigh, N.C., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed June 9, 1966, Ser. No. 556,475 Int. Cl. 133% 31/30; 1329f 3/06 US. Cl. 264-171 2 Claims ABSTRACT OF THE DISCLOSURE The process of this invention produces a self-crimping filament from a common source of polymeric fiber-forming materials by generating two streams of the material at different linear velocities, converging and issuing the streams to form a unitary filament, the streams being of different crosssectional areas but having a substantially equal mass flow rate, and withdrawing the filament at a velocity exceeding that of the individual streams to differentially stretch and asymmetrically orient the filament over its cross section.

The present invention relates generally to the production of synthetic fibers and more particularly to an improved process for the production of filaments having self-crimping capabilities.

In an effort to simulate certain desired attributes of natural fibers, particularly as regards bulk and hand, numerous techniques have been developed to produce texturized synthetic filaments, which techniques generally function to entangle and/or deform a bundle of continuous synthetic filaments to have improved bulk, loft and hand. One long-standing approach may be generally characterized as involving the mechanical deformation of filaments spun in a normal manner; another approach involves the utilization of specific spinning conditions and/ or after-treatments to result in imparting a differential in certain physical properties, particularly shrinkage, over the individual filament cross section.

A more recent approach involves the production of self-crimping fibers having improved crimp characteristics which comprises the spinning of two or more different fiber-forming materials through a common orifice to form multi-component filaments which contain the constituent polymers in an eccentric arrangement over the filament cross section. Suitable after treatments designed to discriminate between certain properties of the filamentary constituents generate eccentric force systems resulting in the formation of a permanent helical crimp. As a variation on this basic approach, it has been proposed to spin self-crimping filaments from a common source of fiber-forming material wherein such source supplies each extrusion orifice with at least two physically discrete streams, which streams have been subjected to differential thermal histories (as regards time and temperature), for example, whereby each stream exhibits, relative to the others, a differential in physical properties, the resulting filament exhibiting an eccentric distribution of component zones supplied by the individual streams; again, suitable after-treatments result in an unbalanced force system over the filament cross section to thereby contort the filament into a crimped configuration.

The general techniques briefly alluded to are encumbered by recognized disadvantages which have prevented a more wide-spread utilization. For example, the mechanical crimping techniques often involve undue filament breakage and damage and are characterized by a low rate of processing relative to that obtainable in the related steps of fiber production. On the other hand, the approaches directed towards a filament exhibiting asym- 3 ,497,585 Patented Feb. 24, 1970 ICC metric physical properties are generally characterized by the necessity of intricate spinning apparatus and lack a high order of product uniformity.

In light of the foregoing problems and limitations, it therefore becomes an object of the present invention to provide a process for the production of synthetic textile fibers having self-crimping capabilities which process imparts a self-crimping mechanism to filaments even in the absence of any differential in herent chemical or physical properties of the two or more constituent streams merged to form such filaments. A further object is the production of self-crimping filaments formed from a common source of fiber-forming material. A further object is the production of such selfcrimping filaments involving only simplified and economical modifications of conventional mono-component spinning systems. Other objects and advantages will readily occur to those skilled in the art in light of the following description.

In accordance with the present invention, the foregoing and still other objects are obtained in the practice of a self-crimping filament spinning process wherein there are produced filaments emanating from the merger of at least two discrete streams of polymeric fiber-forming material, which filaments exhibit an asymmetric differential in orientation over their cross section. This is accomplished by generating the component streams at different linear velocities as they are merged into single filamentary streams and taking up the resulting filament at a linear velocity exceeding that im parted to any of the constituent streams during their passage through the spinnerette capillaries to thereby impart an asymmetric differential in jet stretch over the filamentary cross section; upon suitable after-treatments, normally involving drawing, with or without subsequent heat relaxation or annealing, the asymmetric differential in orientation due to the thus imparted differential jet stretch is manifested by activation of the latent crimp potential due to either or both a differential in elastic recovery of the components (as evidenced by spontaneous crimp development upon drawing) and differential in shrinkage (as evidenced by crimp development upon heat relaxation). It is further comprehended that the self-crimping filaments produced according to the instant process may be spun to exhibit an equality of component distribution over the filament cross section; it has been discovered that this is most readily accomplished by conveying the component streams forming a given filament through passages exhibiting a substantial equality in resistance to flow and imposing a common extrusion pressure upon the component streams. In a most simple and useful mode of practicing the present process, the constituent streams may issue from a common source of fiber-forming polymeric material, which streams are conveyed through passages of equal resistance to flow and of different cross-sectional areas at their exit regions; i.e. in the immediate vicinity of the extrusion orifice.

Though the following discussion of the process will have largely to do with the merger of but two streams to form a given filament, it is to be understood that its practice may as well comprehend the merger of any desired number of streams to form a given filament, though it is unlikely that more than three-component filaments would be so processed; in any event, the same principles and equivalent results obtain. Also, though the preferred mode of practicing our invention involves the use of a single source of polymeric fiber-forming material from which the constituent streams are generated and which may, therefore, entail but a single pump mechanism, it is as well contemplated that multiple fiber-forming sources may be employed, though this latter mode would entail the use of multiple pump mechanisms.

In the preferred mode, the process of this invention involves the extruding of a plurality of unitary filaments from a single polymer source by means of a single metering pump from which the polymer, under a suitable extrusion pressure, is divided into at least two discrete systems of streams, a streamlet from each of the two or more systems then being caused to flow through capillaries of disparate cross-sectional area at their exit region. Preferably, the capillaries supplying a given orifice possess equal mass flow rates to thereby impart a differential in linear velocity of the streams according to the ratio of the capillary cross-sectional exit areas. The capillary :streams converge to cause an eccentric merger of the constituent streams into a unitary filament in the vicinity of a common orifice in which the capillaries normally terminate. The freshly spun filaments are subsequently taken up on a conventional takeup apparatus at a greater linear velocity than the velocity of either stream emanating from the spinnerette orifice. Thus, the freshly spun filaments are asymmetrically and differentially jet-stretched during or immediately after filament formation and prior to complete solidification, with the side of the filament having the lower linear velocity at the spinnerette orifice receiving the greater jet stretch and consequent greater orientation. By virtue of such a sequence, there is imparted to the individual filaments an asymmetric differential in shrinkage properties over the cross-sectional area which results in the formation of a helical crimp, either spontaneously after drawing, or after subsequent heat relaxation. That side or zone of the filament having the greater jet stretch is observed to have the higher shrinkage and/ or immediate elastic recovery after drawing, and is seen to form the inside of the helix of the crimped filaments. Subsequent treating of the as-drawn and relaxed filaments in an atmosphere of dry or humid heat further increases filament shrinkage with consequent enhancement of the crimp level.

This process and certain self-crimping techniques of the prior art are ammenable to combined practice to provide increased crimp development. For example, this process may be combined with that of the previously referred to differential thermal history treatment (wherein the constituent streams forming a given filament are subjected to differences in time and/or temperature during their transit from the polymeric source to the orifice during spinning). The spinning of incompatible polymer blends disclosed in the prior art may also be utilized in the practice of the present process to provide highly crimped filaments. Also, the freshly spun and differentially jet-stretched filaments of this invention may be subjected to asymmetric quenching or solidification to increase or modily the self-crimping tendency thereof, particularly as regards crimp intensity (crimps per inch) and amplitude (as mainly determined by the helix angle and diameter).

Typical polymers which may be utilized in the production of self-crimping fibers by the present process are the polyesters (e.g. polyethylene terephthalate), polyamides (e.g. polyhexamethylene adipamide, polycaprolactam) and copolymers thereof, polyacrylonitrile and its copolymers, polyolefins (e.g. polypropylene) and blends of such polymer compositions.

The degree of crimp development attainable in the practice of this process is contingent upon the polymer composition(s) employed, the degree of jet-stretch to which the freshly spun filaments are subjected during take-up (as well as the magnitude of difference in jet stretch of the components), and the subsequent degree of drawing imparted to the resulting filaments.

In assessing the crimping capability of filaments produced according to the present invention the following test procedure was utilized:

Five skeins of reeled yarn are provided wherein the skein consists of 8 revolutions of the reel and wherein the yarn has been subjected to at least a 0.1 gin/den.

tension to remove residual crimp during skeining. The thusly formed skeins are placed in a tensionless state in water maintained at a temperature of approximately 60 70 C. for a period of ten minutes, then removed from the bath, centrifuged and dried in a tensionless state. Following drying, the skeins are then re-wetted by emersing them for 30 seconds in water maintained at 60 C. containing 2 gm./liter of alkyl aryl sulfonate, a sodium salt wetting agent in the form of No. 1 flake or similar wetting agent. The skeins are then removed from the water, hung on a rack and loaded while wet to provide a yarn tension of 0.200 gm./den. The lengths of the wet stretched skeins are then measured after the load has been applied for 1 minute. This measurement yields a length A in the equation set out below.

After taking measurement A, the weight is removed from the skein and the rack with the skeins in place is placed in an oven for drying at a temperature of 50-60 C. while the skeins are in a tensionless state. After drying, the skeins are placed in a conditioned room maintained at 22 C. and 35% relative humidity for a period of one hour. Following such conditioning, the skeins are reloaded to a tension of 0.002 gm./ den. and their length again measured after one minute of time has elapsed after loading. This measurement yields length B in the following equation.

B A X Percent crimp contraetion= Where:

A:skein length under 0.200 gm./den. load Bzskein length under 0.002 gm./den. load.

Poly(ethylene terephthalate) flakes having a specific viscosity of 0.40 (as determined in a soluiton of 5 gms. of poly(ethylene terephthalate) per 100 ml. of solvent consisting of a 2:1 weight mixture of phenol/trichlorophenol at 25 C.) was dryed in a vacuum atmosphere for a 24 hour period and subsequently melt spun into filaments at an extrusion temperature of 275 C. utilizing the spinning apparatus illustrated in the accompanying drawings.

Such a spinning apparatus, which constitutes the subject matter of our co-pending application Ser. No. 556,- 476 filed June 9, 1966 is seen, viewing FIG. 1, to comprise a spinnerette pack 11 and a spinnerette plate I mounted in face-to-face relationship whereby the internal channeling in the pack and plate are aligned to define continuous passageways. The pack assembly and spinnerette plate are held in the aligned relationship by a suitable holder indicated by phantom outlining. Referring to the details of the spinnerette plate 1 as depicted in FIGS. 1, 2 and 3, such plate is seen to take the form of a circular disc having substantially parallel surfaces, viz the up per or interface surface 6 and lower or exterior surface 15. A plurality of converging pairs of capillaries 2 and 3 are provided in the plate wherein capillary 2 is provided with a larger cross-sectional area, at least at the orifice region, than that of capillary 3. The arrangement of the two groups of capillaries supplying each of a plurality of orifices may take any desired configuration, that of concentric circles being illustrated.

Where it is desired to produce a filament formed from equal amounts of, for example, two streams, means are provided to assure substantially the same mass flow rate through each capillary of a given pair of capillaries supplying a given orifice. Thus, in the instance of the capillary having the larger cross-sectional area at the exit region, resistance to flow means is provided in the polymer flow paths to insure an equalization of the mass flow rate with that of the capillary having the smaller cross-sectional area.

This equality of resistance to flow and inequality of exit cross-sectional areas may be accommodated by numerous arrangements. In the illustrated embodiment, where the large and small pair of capillaries supplying a given orifice are each of uniform cross-sectional area throughout their length, the preferred equality of flow resistance is accommodated by a modification of what is otherwise a conventional bic-omponent spinnerette pack. Such a modified pack 11 is seen to consist of a circular element having two concentric annular passageways 13 and 14 formed therein to interconnect between a polymer source 12, which may take the form of one, two or more distinct sources, which source(s) are forwarded through the spinnerette assembly utilizing a conventional gear-type meter pump, not shown.

Where a single polymer source is utilized, annular passageways 13 and 14 divide the mother stream into a pair of streams, each supplying one of the two groups of capillaries, large and small. That polymer distributed through annular passageways 13 is passed through a filter screen 9 into a distribution passageway 4 which serves to supply the plurality of small cross-sectional area capillaries 3. Annular passageway 14 has disposed therein a filter screen 7 of preferably finer mesh than that of screen 9 and a small amount of size A sand granules overlaid by two additional filter screens 8. This combination of screens and sand provides the resistance to flow required to insure substantially equal mass flow rates through each member of each pair of capillaries. The polymer passing through annular passageway 14 flows into distribution passageway 5 to supply the plurality of relatively larger cross-sectional area capillaries 2.

The polymer flowing through such a spinnerette assembly is thus divided into two separate streams, each of which is extruded through capillaries 2 and 3 of equal resistance to flow with the linear velocity of the polymer passing through the larger cross-sectional area capillary 3 being less than the linear velocity of the polymer being extruded through smaller capillary 2. The polymer streams are merged into a unitary filament exhibiting a. side-by-side relationship and, after passing from orifice 16 are taken up at a higher linear velOcity than that of either stream as they emanate from orifice 16.

The angle subtended between a given pair of capillaries has not been found to be critical over a wide range, the only limitation being that the angle not be so great as t induce undue turbulence at the point of merger which may result in an undue amount of blending between the constituent streams. In certain instances, especially where separation of chemically disparate components in the final filament is observed, it may be desired to provoke a controlled amount of blending between the constituent streams during during the extrusion process, which is to recognize that the angle of merger of the constituent stream supplying a given orifice is not an essential aspect of our process and may vary over wide limits.

Utilizing the illustrated spinning apparatus, wherein the spinnerette contained orifices supplied by pairs of large and small capillaries having cross-sectional exit area ratios of 4: 1, extrusion was affected at a differential in constituent flow velocities of substantially 4:1. The as-spun filaments were taken up at a rate of 593 ft./min. at a point sufficiently downstream to insure substantial solidification to provide filaments exhibiting differential orientation due to a differential in jet-stretch according to the following tabulation:

The spinnerette configuration is such that the two capillary streams are united into a unitary filament in a sideby-side relationship as they emanate from the orifice. The large diameter stream is thus caused to be subjected to a jet-tsretch of 4 times that of the smaller diameter stream to thereby impart different crystalline and shrinkage properties over the cross-sectional area of the filaments, resulting in the subsequent development of a helical crimp throughout the filament length.

After take-up, the filament bundle was drawn at room temperature (22 C.) at a draw ratio of 4.6:1 to provide filaments having a tenacity of 4.9 gm./den., an initial modulus of 82 gm./den., and an ultimate elongation of 19.4%. The filaments were observed to contract 70% and the filaments exhibited a crimp frequency of 12 crimps/inch.

EXAMPLE II The spinning apparatus of Example I was modified to incorporate substantially identical sand pack for each of the passageways 13 and 14 and a second metering pump to extrude the two separate streams of an identical polymer. In all other respects the spinning apparatus was the same.

Utilizing the same polymer composition as in the previous example, a plurality of filaments were spun through a spinnerette containing a plurality of pairs of capillaries wherein one capillary was 0.031 inch in diameter and the other 0.062 inch in diameter at their points of exit. The polyethylene terephthalate polymer was melt extruded at a temperature of 320 C. with each metering pump providing a throughput of 6.0 cc./min.

The following tabulated conditions were observed in the filaments.

Capillaries 0.31 0.062" diameter diameter Theoretical capillary linear throughput (it./

20.8 5.2 3,100 3,100 Theoreticaljet-stretch 149 596 EXAMPLE III Utilizing the apparatus of Example II, polyethylene terephthalate filaments were spun at a melt extrusion temperature of 320 C. The two meter pumps provided a throughput of 6.0 cc./min. each and the take-up speed was reduced to 1930 ft./min.; hence, the two sides of the unitary filaments were theoretically jet-stretched 93 and 372 times, respectively.

Part of the as-spun yarn was subsequently drawn over a hot pin maintained at C. at a draw ratio of 2.0:1 while the remainder was drawn utilizing the same draw pin temperature at a draw ratio of 4.0: 1. The yarn drawn at a 20:1 draw ratio had 45% crimp contraction while the yarn drawn at a draw ratio of 4:0:1 had 39.4% crimp contraction.

EXAMPLE IV Polyethylene terephthalate filaments were produced with the same apparatus and in the same manner as those in Example II with the exception that the extrusion temperature was maintained at 295 C. The as-spun filaments were taken up at 3100 ft./min. and were subsequently drawn at a ratio of 2.0: 1. The as-drawn yarn exhibited a crimp contraction of 54%.

7 EXAMPLE v The spinning conditions of Example IV were utilized to produce a polyethylene terephthalate yarn by means of the same apparatus. The as-spun yarn was taken up at 1930 ft./min. which provided a jet-stretch in one side of the filament of 93 and a jet-stretch in the other side of the filament of 372. Subsequent drawing of the yarn over a hot pin maintained at 100 C. and at a draw ratio of 2.5 :1 resulted in a crimp contraction of 53%.

EXAMPLE VI Polypropylene polymer was melt-spun i the same manner and with the same apparatus as employed in Example II. The polymer was extruded at a temperature of 323 C. and the as-spun filaments were taken up at 1570 ft./min.; hence the two sides of the unitary filaments were subjected to a jet-stretch of 75.4 and 301.6 times respectively.

The yarn was subsequently hand drawn in ambient atrnosphere resulting in the yarn exhibiting a small degree of spontaneous crimp, i.e. a crimp developed spontaneously upon the release of drawing tension and without subsequent heat relaxation.

EXAMPLE VII Polyhexamethylene adipamide polymer having a relative viscosity of 43 (as determined in a solution containing 8.4 wt. percent polymer in 90% aqueous formic acid at 25 C.) was melt spun into a plurality of filaments in the same manner and with the same apparatus as that of Example II with the exception that the extrusion temperature was maintained at 290 C. and the take-up rate was 3100 ft./min. Samples of the as-spun yarn were subsequently hand drawn at ambient conditions resulting in the relaxed yarn exhibiting a small amount of crimp.

In light of the foregoing, it may now be appreciated that there has been herewith disclosed a novel and beneficial process of producing filaments possessing a selfcrimping potential involving very simple and easily controlled modifications of otherwise conventional spinning equipment. This technique of converging two or more streams having a differential linear velocity through a common orifice and taking up the resulting filament at a linear velocity greater than any constituent stream velocity to provide a filament having an asymmetric differential in jet-stretch and a consequent differential in orientation to thereby establish a differential in elastic recovery on drawing and/ or a difierential in residual shrinkage has been found to be of most beneficial application. As may readily be understood, numerous variations and modifications may occur to those skilled in the art ap pertaining hereto in light of the above teachings. It is, therefore, to be understood that, within the scope of the appended claims, the invention may be practiced otherwise and as specific-ally described herein,

What is claimed is:

1. A process for the production of self-crimping filaments comprising generating at least two streams of polymeric fiber-forming materials, said streams being of the same polymeric material, at different linear velocities, said streams having different cross-sectional areas and equal mass flow rates, converging and issuing said streams to form a unitary filament, withdrawing said filament at a velocity exceeding that of the individual streams to differentially stretch and asymmetrically orient said filament over its cross-section.

2. A process for the production of self-crimping filaments comprising generating at least two streams of polymeric fiber-forming materials, said streams being of the same polymeric material, at different linear velocities, said streams having different cross-sectional areas by passing said streams through flow passages having exit portions of different cross-sectional areas, said stream having the lower exiting velocity and issuing from the passage having the greater cross-sectional area being subjected to a flow resistance in said passage to meter the volume of said stream to equalize the mass flow rates between said streams, converging and issuing said streams to form a unitary filament, withdrawing said filament at a velocity exceeding that of the individual streams to differentially stretch and asymmetrically orient said filament over its cross-section.

References Cited UNITED STATES PATENTS 3,399,259 8/1968 Brayford 264168 3,408,277 10/1968 Martin et al. 264168 3,095,607 7/1963 Cobb 188 2,804,645 9/ 1957 Wilfong. 2,900,708 8/1959' Pond. 2,968,834 1/1961 Groombridge et al. 264103 X 2,980,492 4/1961 Jamieson et al. 3,073,005 1/1963 Tiede 28-82 3,117,362 1/1964 Breen 57-140 3,161,914 12/1964 Bloomfield et al. 264-168 X 3,264,390 8/1966 Tanner 264171 3,315,021 4/1967 Luzzatto.

FOREIGN PATENTS 1,431,147 1/1966 France. 1,434,801 2/1966 France.

6415124 8/ 1965 Netherlands.

624,280 4/ 1963 Belgium.

JULIUS FROME, Primary Examiner I. H. WOO, Assistant Examiner US. Cl. X.R. 264168 

